Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Schedule of Cost-method Investments [Line Items]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	$ 4
Interest Rate Caps Sold
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount	7,400	$ 8,200
Purchase [Member]
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount	2,300	2,000
Interest Rate Cap [Member]
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount	9,736	10,179
Interest Rate Cap [Member] | Subsidiary Issuers
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount	5,100	6,200
Interest Rate Swap [Member]
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount	1,950	900
Currency Swap [Member]
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount	$ 692	$ 811